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The Phanerozoic Eon • 542 mya – Present • Divided into 3 Eras – The Paleozoic, Mesozoic, and Cenozoic Eras • The ends of the Paleozoic and Mesozoic Eras were marked by mass extinctions • The Cenozoic Era is still continuing today Nov 2810:32 AM Jan 2210:12 AM 1 The Paleozoic Era • 542 – 250 mya • Began with the Cambrian Period and ended with the Permian Period • The Paleozoic Era was marked by the evolution of most modern animal phyla, the formation and break‐up of several supercontinents, and the colonization of land by plants and animals Nov 2810:32 AM The Cambrian Explosion • With the uptick in atmospheric O2 at the end of snowball earth, multicellular life began to evolve extremely rapidly • Within a few million years, organisms began to develop mobility and the first modern animals were born • Future generations began to evolve features like teeth and claws that allowed them to become more successful hunters and their prey followed suit by developing defensive structures like shells Nov 2810:32 AM 2 The Cambrian Explosion • This “arms race” fueled evolution’s progress and within 20 million years of the beginning of the age, all present animal phyla had evolved • This event that marked the 20 million year span of rapid evolutionary development is known as the Cambrian Explosion • The best place in the world to see evidence of this is the Burgess Shale in the Canadian Rockies of British Colombia Nov 2810:32 AM Nov 2810:32 AM 3 Nov 2810:32 AM Jul 291:07 PM 4 Periods of the Paleozoic • Cambrian – explosion of life • Ordovician – adaptive radiation of animal phyla formed during the Cambrian including the formation of vertebrates • Silurian – major arthropod advancements and beginning of land plants • Devonian – invertebrates and amphibians colonized land • Carboniferous – large swamp forests that led to all coal formations today and the development of land reptiles • Permian – proto‐mammals evolved out of reptiles Nov 2810:32 AM The P‐T Extinction Event • At the end of the Permian Period, the climate of the earth began changing • The formation of Pangaea created a super‐desert over much of the land on earth and caused oceanic currents to change altering the weather and rain cycles severely • Then, 250 mya, a super‐volcano in present‐day Siberia erupted causing a “nuclear winter” that lasted years • Many species already in trouble due to environmental pressures caused by Pangaea could not survive the conditions over the next few years and 83% of all genera on the planet were wiped out Nov 2810:32 AM 5 The Mesozoic Era • 250‐65 mya • Marked on both sides by the two largest extinction events in history • The “Age of the Dinosaurs” • The P‐T Extinction at the end of the Permian allowed for massive adaptive radiation of remaining species • Broken into 3 Periods – The Triassic, Jurassic, and Cretaceous Nov 2810:32 AM The Triassic Period • 250‐200 mya • Began at the end of the Permian‐ Triassic Extinction event • Pangaea remained intact throughout the Triassic • The first dinosaurs evolved during the mid‐Triassic including Pterosaurs and the small Coelophysis and their relatives • Advanced Cynodonts gave rise to the first mammals midway through the Triassic as well Nov 2810:32 AM 6 The Jurassic Period • 200‐145 mya • Beginning of Jurassic is marked by the initial breakup of Pangaea into the two supercontinents Laurasia and Gondwanaland • Large herbivorous dinosaurs like the brontosaurus, marine dinosaurs like the ichthyosaurs, and pterosaurs were the dominant dinosaurs at this time Triassic/Jurassic • Mammals were small and insignificant • End of Jurassic was marked by the appearance of flowering plants on earth Nov 2810:32 AM Nov 2810:32 AM 7 The Cretaceous Period • 145‐65 mya • Dinosaurs evolved into their peak diversity during the Cretaceous • T‐Rex, Triceratops, Velociraptor, and modern birds all evolved • Laurasia and Gondwanaland broke up into the today’s continents, but they were not yet in their present positions • The Cretaceous and the entire Mesozoic Era came to an end with an asteroid impact near the present‐day Yucatan Peninsula Nov 2810:32 AM Nov 2810:32 AM 8 The K‐T Extinction • Called the Cretaceous‐Tertiary Extinction event • 65 mya, an asteroid impact threw ash into the atmosphere blocking out most sunlight for years • Most photosynthetic plants died, leaving no food for the large herbivorous dinosaurs that required massive amounts of energy daily • All non‐avian dinosaurs, pterosaurs, and marine reptiles perished along with many other species • When the ash settled, the stage was finally set for mammals to take over the earth Nov 2810:32 AM The Cenozoic Era • 65 mya – Present • The “Age of Mammals” • Continents moved into their present positions • The movement of Antarctica to the south pole and the joining of South America to North America altered oceanic currents and led to global cooling • Forest swamps of the Mesozoic Era gave way to large areas of grasslands in the Cenozoic Era Nov 2810:32 AM 9 The Cenozoic Era • Mammals diverged from a few small, generalized forms to the plethora of terrestrial, marine, and flying types of the present • Birds diversified and flowering plant/insect relationships developed as well • Snakes and modern lizards, the newest reptiles evolved during the Cenozoic • The Cenozoic Era is divided into 3 Periods • The first two are collectively known as the Tertiary, while the last Period is the Quaternary Nov 2810:32 AM Periods of the Cenozoic • The Paleogene Period • 65‐23 mya • The most significant evolution of birds and mammals occurred in the Paleogene • Ended with a minor extinction event affecting mammals • The Neogene Period • 23‐2.5 mya • Creation of the Panama Isthmus and the resulting global cool‐down were the defining events of the period Nov 2810:32 AM 10 Periods of the Cenozoic • The most recent Period of history is the Quaternary (2.5 mya‐ Present) • Marked by the rise of Homo sapiens • Though primates had been evolving since the K‐T Extinction 65 mya, the Homo line had been evolving since the Neogene Period 6‐7 mya • During the Quaternary, Homo neanderthalensis, Homo erectus, and Homo sapiens all fought for resources and interbred until the present form of humans were the only species left by 30,000 years ago Nov 2810:32 AM Nov 2810:32 AM 11 Periods of the Cenozoic • The Quaternary is divided into two important Epochs • The Pleistocene • 2.5 mya ‐ ~12,000 years ago • The Ice Ages • Marked by 11 known glaciations that covered 30% of the earth’s surface at each maximum • Glaciations as well as development and subsequent predation by humans drove most mega‐mammals to extinction • The Holocene • ~12,000 years ago – Present Day • Considered an interglacial period during the present ice ages • All of humanity has occurred in this brief warm period of time, roughly 0.0003% of the history of the world Nov 2810:32 AM Nov 2810:32 AM 12 Eons Eras Periods Epochs Archean Cenozoic Permian Holocene Proterozoic Mesozoic Cretaceous Pleistocene Phanerozoic Paleozoic Quaternary Hadean Jurassic Triassic Tertiary Cambrian Nov 2810:32 AM 13
